Seperation of Sexes

[aman]

I'm curious as to wether the early macrophages were the instruments of the first evolution of sexes. Since they carried different DNA it may have been advantageous to transfer them from one bacteria to another.

Just aman

[Ahmad]

I would assume evolution went this way:

 

asexual organism -> bisexual organism -> sexual organisms

 

Hydra, for example, was capable of doing all three types of reproduction: asexual reproduction, self-fertilization, and cross fertilization.

 

Asexual reproduction was achieved in hydra by its ability to regenrate into complete organisms if they were chopped into pieces. As organisms grown in size and had more specialization, this became impossible to achieve, so the ability was lost.

 

But why did organisms lose their bi-sexuality? I don't know.

[Giles]

Contemporary possible 'intermediate stages' in 'bacteria sex':

 

1. Transformation and plasmids.

Bacteria can take up and release small loops of genetic material called plasmids, and while inside the bacterium these can be treated as part of its genome, and even reproduce with the cell. A bacteria that takes up a plasmid is said to be 'transformed'.

 

2. Conjugation

Certain bacteria have external structures called pili (from the latin for spear). When the pili of two bacteria of the same species meet, if certain other conditions (chemical signals etc.) are met, the two fuse, and the cytoplasms of the two cells become continuous, allowing plasmid exchange.

 

3. F+ and F- e. coli

(I think that's the right terminology). A certain Eschera coli plasmid will lead to conjugation when one cell with it and one cell without it come into contact, the F- cell being transformed to F+ when it receives the F plasmid. This is not unlike having two sexes.

 

So it's not that hard to see how single-celled organism might have acquired sexual characteristics. Unfortunately its hard in the fossil record to see what actually happened.

 

There is an intermediate stage between being unicellular and multicellular - so called 'colonies'. Famous example is the portugese Man o'War 'jellyfish'. Another type that has made waves recently is slime moulds, colony organisms formed by eukaryotic unicellular organisms under conditions of food scarcity. With one of these incorporating something like the 'sexual' bacteria, you can see how specialist structures would be favoured much as they were for every other function. Transformed components could then begin to form another organism, which of course encourages wombs an so on...

 

This raises the question of the two physiological different sexes we have. This is a question of 'evolutionary stable strategies'. If the two sexes make a substantial contribution to the young's survival, there is an advantge to be had making a smaller contribution to more offspring. You would get an 'arms race'. Furthermore, this would encourage other differences because if two individuals made a low contribution to the offspring's survival it would probably die. This also raises the pressure for the highly contributing parent to contribute even more care, and eventually the situation polarises. So you have division into male (contributes sperm) and female (contributes egg and care), and both sexes avoiding mating with themselves, until eventually they can't.

[NavajoEverclear]

after losing the attention span to read the last few posts i think i'm probably to uneducated to make competent coments on the subject but i will anyway. I'm not sure if Blikes question was ever answered--- how does sexuality evolve from an a sexual organism (that's how it started right?) is it just some random mutation, or what is it? How does it happen? And then once it does happen, like blike said how does it become advantous--- think about it , you have one sexual cell (however it became this way) in the midst of all the asexual ones. It cant USE its sexuality, it doesn't have any effect on the asexual. Does it somehow search out another sexual cell? Or does it just die and billions of sexual mutations occur until two find each other and begin producing a sexual population.

 

I as i was brought up religiously, have come back to choose to still hold those beliefs. I find it ridiculously bothersome when people of religious tendancy defend their beliefs with made up proof just because they really feel they are obligated to defend them. That is not true faith, so try to be openminded. I do believe evolution occurs at least on a certain degree, but that was not the course God took. I mean anyway we don't really have any proof of cells evolving into animals, yes i understand the complexity of mutations and natural selection fairly well, so i have to admit i see evolution is possible, but there are lot of things about it so far as evidence not found (to me anyway). Like why aren't there just as many intermediary species between apes and humans, infact, why would there be any distinct species at all, because evolution is gradual, or are there jumps? Or how does this work? Actually ignore my latter questions until later. Put the first paragraphy in priority to resolve those things.

[Kettle]

I just dredged this article up:

 

http://news.bbc.co.uk/1/hi/sci/tech/specials/sheffield_99/447058.stm

 

it doesn't so much explain why we have 2 sexes as why we don't have several thousand

 

[NavajoEverclear]

That was an extremely intersting article, thank you for the input. I don't know about that bacteria become part of us, maybe so, i just don't know. So how do 36,000? sexes work? do they just spread their spores or whatever and multiple spores interact to create some mix? I really don't understand that at all. I see we only have two sexes because thats as simple as it can be, and why should it be any more complicated? i don't see how complication is an advantage, two sexes works fine, just make, how would more make us more diverse? I guess i'd have to understand how more than two sexes even works to ask that question.

[Kettle]

I think that the advantages with lots of sexes all comes down to maths. To quote the article:

 

If we had a hundred sexes, and could mate with any one of them, our chance of finding a partner in our surrounding environment would be 99%....If there are only two sexes, then on average, half the time the person you meet is not going to be a potential mate

 

But with multiple sexes comes a higher possibility and risk of mutation so it really comes down to a balancing act.

 

Sorry - I'm just paraphrasing the article but I hope that explains why a more complicated group could be considered beneficial.

 

Edit:

Something has just occured to me - aren't mushrooms really just the fruiting body of a funghi? So they're not really an organism in their own right...?

[Skye]

My statement was only valid with non-functional, intermediate structures.

It's kind of been said before but..there's really no 'need' for useless intermediate structures. The seperate sexes descended from bisexual, hermaphroditic organisms that had both sets of reproductive organs. A variant of a single sex would be able to reproduce with the existing hermaphroditic population. It's not hard to see 'how' it could have happened, but 'why' it would remain a puzzle...I think seperate sexes, as well as sex itself, has developed a few times (at least in both animals and plants seperately) so there could be several individual reasons.

 

Also our reproductive process is complex compared to, say bacteria, but delightfully simple compared to alot of invertebrates that have alternating sexual and asexual generations.

 

In the case of the man o' war (a jellyfish with a ballon-like 'float' that helps it stay on the surface) the jellyfish is actual a colony of many polyps (each is an individual multicellular organism). These are asexually produces from a single worm-like predecessor called a planular. One enormous polyp forms the float, many form the food gathering tentacles, and also many form reproductive tentacles. These reproduce sexually, so the cycle goes: planula asexually produces jellyfish which sexually produce planula.

 

This is a very complex cycle, and perhaps a single sexual cycle would have some advantages....

[Radical Edward]

Originally posted by Skye

In the case of the man o' war (a jellyfish with a ballon-like 'float' that helps it stay on the surface) the jellyfish is actual a colony of many polyps (each is an individual multicellular organism). These are asexually produces from a single worm-like predecessor called a planular. One enormous polyp forms the float, many form the food gathering tentacles, and also many form reproductive tentacles. These reproduce sexually, so the cycle goes: planula asexually produces jellyfish which sexually produce planula.

 

are all these literally seperate, but genetically identical organisms then?

[Skye]

Yeah, each is a seperate asexually produced 'clone', genetically identical to both each other and to it's parent planula. I'm guessing the planula starts asexual reproduction by dividing into two seperate organisms, there're two ways that I know Cnidarians (jellyfish, coral, sea anemones) asexually produce and the other is by budding off a smaller copy...doesn't makes as much sense. Either way it develops something like an embryo, contantly increasing in number and differentiating BUT each part is a multicellular clone.

 

Man o' war jellyfish belong to a different class to other jellyfish (it's class Hydrozoa, the others are in Scyphozoa and Cubozoa) and are very different. There's two stages of the lifecycle in Cninarians, polyp and medusa. The man o' war jellyfish is the colonial polyp stage. Other jellyfish you see are the singular medusa stage, the polyp stage is sessile, attaches to the bottom of coastal areas and asexually produces larvae that turn into the medusa stage.

 

 

As I said our reproductive systems are delightfully simple comparitively. But also there are intermediate reproductive systems that could have produced the two seperate sexes.

[Kettle]

So do you know how mushrooms with 36,000 different sexes fit into all this? How do they reproduce and what (in a generalised way obviously) are the essential differences between sexes?

[Sayonara]

Mushrooms are the spore-bearing structure of a fungus, and fungi have a fairly different biology to animal and plant cells.

 

It's been a while since I had to think about this subject, arrrgh...

 

Fungi can reproduce both sexually and asexually at the same time. As far as I know they do not in fact have 36,000 genders - in fact I'm not sure they have genders at all. Remember that sexual reproduction requires recombination of genetic material from two individuals, not necessarily from a "male and a female", terms which are meaningless when you are dealing with unicellular organisms or the true hermaphrodites.

 

I can't actually remember how fungi reproduce sexually (fungi = dullness) so I'll be back with more info!

[Sayonara]

http://www.sporometrics.com/notes.html

Asexual vs. sexual reproduction

 

Most fungi have more than one means of reproducing themselves. The most elaborate method is typically sexual reproduction, which involves the mating of two strains (or often one strain with itself). Sexual reproduction produces recombinative spores called either ascospores, basidiospores of zygospores, according to the division to which the fungus in question belongs (the Ascomycota, Basidiomycota or Zygomycota, respectively).

 

Many fungi may be reproduced more simply than this, however. It is often possible to take a fragment of a hypha or a bit of mycelium from a colony, place it on a nutrient medium and with a little time obtain a new fungus colony. This is usually the preferred method for reproducing fungi in the laboratory. A great number of fungi rely on this simple means of colony fragmentation for reproduction in their natural habitats. In fact, the success of asexual reproduction has driven the evolution of a wide variety of modified hyphae that simply break apart to facilitate dispersal.

 

Asexual reproduction is so successful that some fungal species have simply ceased to undergo sexual reproduction. A similar trend is common in certain plant species which have lost the ability to flower and reproduce themselves by runners, tillers, rhizomes and various kinds of fragmentation. Since the classification of fungi (like plant classification) is based upon the form of the sexual reproductive structures, it has been difficult to integrate fungi which no longer exhibit sexuality into the traditional classification scheme. Thus, a special division called "Deuteromycota" was set up to accommodate these fungi.

 

Unlike the other fungal divisions, the Deuteromycota is not organized according to relationship (shared ancestry), but rather it is based solely on form. As such is often termed a "form division". Most of the fungi we commonly think of as "moulds" belong to this division, and are known only from their asexual forms (anamorphs). The true affiliation of these asexual fungi is often clear, however. In fact, the majority of moulds are known to be asexual states of members of the division Ascomycota.

[Kettle]

Blimey - well done for finding that

[Sayonara]

Originally posted by Kettle

Blimey - well done for finding that

Wasn't as easy as I thought it would be.

 

Putting "Fungal" and "Reproduction" into Google turns up some yucky results

[blike]

recombinative spores called either ascospores, basidiospores of zygospores,

 

truffles are basidiomycetes.

 

Thats about all I remember from bio2 last semester. :zzz:

[Skye]

The fungal reproductive cycle as I know it has three stages: haploid, dikaryotic and diploid. Most of a fungus is mycelia that grow under the ground, or into their food eg. bread moulds. The mycelia start off haploid. When they meet another mycelia they can fuse to form a single cell, but the nuclei remain seperate within the cell. I've also read that they can exchange nuclei but not sure on that. This cell with two seperate haploid nuclei is called dikaryotic. Two haploid hyphae cells can only fuse with certain others. Basically it's one that doesn't have the same gene as a particular locus. The simplest fungi have a single locus this acts on and only two alleles at that loci, so they have two 'sexes'. Others have 2 (maybe more) loci, and many different alleles at each. The 36,000 sexes (I think this is the highest number but other have thousands of these sexes) are just the many variants at these loci.

 

Why have 36,000 sexes? With two sexes the chances of meeting a mate are halved, because every second one is identical. With 36,000 the chances of meeting another just like you are practically zero.

 

The other thing is that the dikaryotic hyphae produce mushrooms. In the mushrooms the two nuclei fuse which briefly forms the diploid stage, but pretty quickly undergo meiosis and form the haploid spores which blow away and form hyphae. During the meiosis there's the usual crossing over and all that good stuff which produces variation.

 

Soooo each haploid hyphae is able to fuse with half it's siblings, since they inherit one of their two parents 'sexes'. If there are only two sexes in the species then it is able to fuse with half of them too. If there are many more (like 36,000) then they are able to mate with pretty much anyone they come across, but still only half of their siblings. Fungi aren't very motile, and quite likely to come across their siblings, the 36,000 sexes would help in allowing them to mate with most other hyphae that aren't siblings and increase outbreeding.

[Sayonara]

Thanks Skye!

 

Exactly what I was trying to find.

[Guest themusicman]

i believe that the seperation of sexes is a bunch of bs

[Guest themusicman]

anyone know anything about the seperation of sexes?????

[Guest themusicman]

come on im working on a school project and need some help PLEASE HELP ME NOW

[Martin]

The first sexually reproducing organisims were in fact microbes (approximately 2 billion years ago). This eliminates complex systems for sexual reproduction that would take many generations to develop. So my basic understanding is that the first occurance of sexual reproduction would have been very simple and crude and then developed from there.

 

I got my info from Carl Sagan's Cosmos.

 

I think what you say sounds reasonable---about the 2 billion years---the single cell organisms.

 

it would have been a good strategy.

 

I read something 10 years or more back about some kind of mold or yeast having sexes----it did some fairly complex dealie to mix its genes up and went thru a fairly complicated reproductive routine----it had more than 2 sexes.

 

And back in high school we were told about paramecia coupling up and trading some genes and then both of them going off and dividing. I dont know if that is true. It is not sexual anyway because it is hermaphro, or unisex, or something.

 

 

the main thing about M/F difference, down at the very primitive cell level, is that only the Female Mitochondrions survive.

 

the sperm has mitochondrions which are the fuel cells or batteries, but when it goes into the ovum then the sperm's mitochons self-destruct or something.

 

otherwise, if the sperm and the ovum were the same size and both wiggled then you could not tell which was which-----the difference is what happens to the mitochons when they merge.

 

If you had 3 sexes, like some Yeast colonies might, then what would define them would be whose mitochons survive. Suppose this. Suppose three types A, B, C.

 

A screws with B (B's mitochondria win)

B screws with C (C's mitochondria win)

A screws with C (C's mitochondria win)

 

So we would say that A is male

and B is semifemale

and C is extremely female.

 

this is how I remember, but the yeast actually had more than 3 sexes and I am simplifying.

 

Anyway, sex is very old, and it is related to death. Death evolved too.

 

if you want to benefit from sex constantly mixing the genes then the old models have to die so the newly mixed editions get to be tried out.

 

the genes do all this for their own good.

they invent sex

they invent death

 

they foist these nifty inventions on us

 

OOOPS! I didnt see SKYE ALREADY SAID THIS BETTER!!! sorry

[Martin]

...

 

Soooo each haploid hyphae is able to fuse with half it's siblings' date=' since they inherit one of their two parents 'sexes'. If there are only two sexes in the species then it is able to fuse with half of them too. If there are many more (like 36,000) then they are able to mate with pretty much anyone they come across, but still only half of their siblings. Fungi aren't very motile, and quite likely to come across their siblings, the 36,000 sexes would help in allowing them to mate with most other hyphae that aren't siblings and increase outbreeding.[/quote']

 

that is really neat

 

what I remember hearing of was a fungus or something that had 9 sexes.

I didnt want to say it in my post because it sounds so incredible, so I used a simplified example with 3.

 

I had never heard of having 36,000 sexes. that would be wonderful. it is extremely clever. fungus have more fun. in my next life shall be an intelligent fungus

 

do you know anything about the evolution of death? why it evolved etc.

[Skye]

A very small part of your body (no offence) will hopefully live for ever. These are your germline cells, and they are not designed to die. But the rest of your cells, while they can reproduce, cannot produce a new organism. Their sole purpose is to aid those cells that are able to reproduce. Once this task is over, they have no purpose at all, and quite promptly die.

[Martin]

A very small part of your body (no offence) will hopefully live for ever. These are your germline cells, and they are not designed to die. But the rest of your cells, while they can reproduce, cannot produce a new organism. Their sole purpose is to aid those cells that are able to reproduce. Once this task is over, they have no purpose at all, and quite promptly die.

 

BTW have to compliment everybody on this thread. Apologize for my redundancy too. I happened on it by accident yesterday and immediately responded to an early post by dronezero---turned out everything I had to say (or almost) was said better by others. Should have read the whole thread before responding to the early post on it.

 

lot of very interesting stuff came out in this thread.

 

I am still unclear about the precise evolutionary reason that death had to evolve. If there were infinitely many stars with habitable planets and cheap means of travel then people could simply stay young forever and continue reproducing, could they not. So is death advantageous because of finiteness of the environment? Advantageous for whom?

 

You say "Their sole purpose" but after one has begotten one child or two children then what is the "purpose" of senescence and death? why not continue reproducing indefinitely, if the original "purpose" is OK?

 

apparently it is to the genes advantage that their carrier stop reproducing and die

 

otherwise ageing would not have been invented by evolution and programmed into sexually reproducing organisms.

 

I am trying to think about this from the standpoint (not of "purpose" which is a bit slippery concept but) in terms of *advantage* of genes. I want to see it from the genes point of view.

 

At what point in the history of life do you suppose that built-in aging mechanisms evolved? Were the aging mechanisms invented at around the same time that sexual reproduction was invented?

 

BTW I dont agree that I have immortal cells in my body. When two persons genes scramble and produce a new combination it is a whole new genetic recipe and the cells are different-----the only approximation to having immortal cells would be to reproduce by cloning. So if you mean cells, then I have no immortal part in my body. So even though i can tell you know a hundred times more than I do about this, I disagree with that part of what you say.

 

Amoebas, I guess, are immortal. they dont age, AFAIK. they must have evolved before life got the notion that it would be a good idea to age and programmed it in.